The invention relates to a unit module for a high-frequency antenna for receiving or transmitting a rectilinearly polarized wave, comprising radiating elements in the form of horns and a power supply network assembled from waveguides of rectangular cross-section connected to the horns and also interconnected such that for each horn the total overall length of the supply path is the same.
The invention also relates to a high-frequency antenna comprising such unit modules.
The invention is used, for example, in making planar antennas for receiving television broadcasts which are transmitted via artificial satellites.
An antenna comprising radiating elements in the form of horns fed by waveguides is disclosed in the Patent Specification DE 2641711 (corresponding to Great Britain Patent Specification 1,584,034), which describes a linear antenna module, formed by a row of horns which are manufactured in one glass fibre block with metal-plated surfaces. This row of horns is supplied by a main line and also by individual lines connected to the main line. The main line has a rectangular cross-section, is made from aluminium and may be filled with a dielectric material. This main line is realized such that in the plane of the electric field E it constitutes a multi-stage power divider by means of which it is possible to supply at equal powers the waveguides which provide the individual connection of the horns to the main line. Each of these waveguides, of rectangular cross-section, is constituted by a laminated structure having a dielectric material provided between two copper layers, the edges of this structure being metal-plated. The length of the individual supply waveguides and also the point in which they are connected to the main line are chosen such that for each horn the length of the supply path formed by the main line and the individual supply line will be the same. Such a structure has for its object to enable phase differences to be corrected in the supply of the horns by reducing the length of certain individual power supply lines.
However, such an antenna has several disadvantages. First of all it has of necessity very high losses since the propagation of the waves in a dielectric medium such as the medium constituted by the laminated structure of the individual power supply lines of the horns is always subjected to high losses, even if the dielectric material is of a very good quality. Using an identical dielectric material in the main line increases the losses still further. Adding to that is the fact that the price of a high-grade dielectric material is always very high and considerably increases the cost of the antenna.
Moreover, the antenna module described in the document is of a linear shape, and is supplied in series, because of which it is actually very difficult to obtain an accurate in-phase supply of the horns and it is therefore absolutely necessary to effect a length adjustment of the individual supply lines to improve this result. It remains however difficult to obtain an accurate in-phase supply of all the horns when a wide operating frequency band is required. In addition, the solution suggested by the documents to solve this problem, results in a very complicated shape of the antenna, and also in an assembly and adjusting procedure which are too critical to have them effected during, for example, large-series production.